What is PNS 49?
How
do I know if the steel bars I buy conform to PNS 49?
Where
can I have my steel bars tested?
Why
is it important to have standard steel bars?
What
are some practices that should concern a buyer?
How
do you measure the diameter of a ribbed bar? Does it refer
to the core or the ribs?
Does
rusting affect the performance of reinforcement?
What
is the smallest bend radius that we can bend a bar?
What
is PNS 49?
Steel bars are covered by a mandatory standard called the Philippine
National Standard 49 or PNS 49, as formulated by the Bureau of Product
Standards (BPS) of the Department of Trade and Industry (DTI) with the
help of the Steel Industry, the Association of Structural Engineers
of the Philippines, and the Philippine Construction Association.
How
do I know if the steel bars I buy conform to PNS 49?
Check if the manufacturer is accredited by the Bureau of Product Standards
(BPS). All manufacturers accredited by the BPS are required to place
their distinguishing logo on every meter of their steel bars. The logo
is registered with the BPS. However, a manufacturer can still attempt
to circumvent PNS 49 despite its accreditation. Always have two or three
specimen steel bars tested in a reputable laboratory. The laboratories
will measure, weigh and test the yield point, tensile strength, elongation,
and bending of the steel bars. One cannot ascertain the quality of a
steel bar simply through visual inspection.
Where
can I have my steel bars tested?
Your sample can be tested either at the Metals Industry Research and
Development Center (MIRDC) in Bicutan or the Philippine Geoanalytics
in Quezon City to see if it conforms to PNS specifications.
Why
is it important to have standard steel bars?
In an earthquake prone country like the Philippines, the use of substandard
steel bars can be life-threatening. The yield point and tensile strength
ratio ensures that there is enough "reserve energy" for the steel you
use to withstand the sustained swaying motions and the subsequent aftershocks
of an earthquake.
What
are some practices that should concern a buyer?
One common practice is to maximize the 6% weight tolerance allowed by
PNS 49 for each steel bar. Since weight deviations of 2% - 3% occur
during the rolling process, undersized steel bars are included in the
production batch. Another practice is the use of unsuitable raw materials
to produce steel bars that are too brittle and cannot pass bending tests
under laboratory conditions. Still another practice is passing a lower
grade off as a higher grade by switching the color coding of the steel
bar. A rule of thumb is never to buy from a manufacturer whose selling
price is more than 2% lower than other competitors. The savings involved
are not commensurate to the risk.
How
do you measure the diameter of a ribbed bar? Does it refer
to the core or the ribs?
The nominal diameter of a bar, say 16 mm, refers to the mean nominal
diameter of the total cross sectional area of the bar. That is, it is
a theoretical diameter which cannot be accurately measured using a rule,
caliper or micrometer. It can only be measured by accurately weighing
and measuring a length of bar and calculating the mean diameter from
these measurements.
Does rusting affect the
performance of reinforcement?
Surface rusting of reinforcing bars or mesh does not effect the performance
of the steel. In fact, surface rusting can increase the bond of the
steel to the concrete. However, prolonged surface rusting can eventually
lead to pitting of the steel and this may lead to a weakening of the
steel section. Suspect steel can be checked by weighing a cleaned sample
to check that the section is not below the lower unit mass tolerance
and tensile testing undertaken to ensure that the physical properties
are still above the minimum requirements.
What
is the smallest bend radius that we can bend a bar?
The PNS 49 Standard sets out the minimum pin diameter for the bend radii
of the various sizes and grade of rebars. See PIN DIAMETER in our Technical
Specifications.
Glossary
of Terms